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(SOLVED)Basic circuitry

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Originally posted by: TuxDave
Voltages look ok, the BJT is on and you're driving it hard so the circuit is working. All you have to do now (if your goal is to get this BJT saturated and get Vce = 5V is to slow tune the pot. Keep monitoring VCE as you adjust it and top when it hits 5V. The resistance between T2 and T3 should be much higher than T1 and T2 in case you're not sure which way to tune.

You know why right?
Click to expand...

That tidbit really provided helpful. Now it works... Thanks.
Resistance of T1-2 = 88.8k ohms
Resistance of T2-3 = 8.0k ohms

As for why... is it because the transistor is acting as a dependent current source? Other than that, I'm not sure since what I expected the resistances to be was purely the opposite.
 
More or less right. The Ice is a current source that is a function if Ibe (in saturation). Vbe is stuck at around 0.7V due to its diode connection so if you had the pot set halfway such that you get a significant amount of current across your 20Kohm resistor, Ice will be as large as it can which is why Vce was very close to zero.

By changing the voltage divider, you are slowly reducing the current flowing into the base which should reduce the current in the collector and eventually bring it to 5V if you tweak it right.
 
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